106 Scientific Proceedings, Royal Dublin Society. 



taken and put through the same series of tests as was the nickel wire, and 

 though the presence of the nickel wire in the gap of the iron tube will 

 increase the magnetic field, whereas the presence of the copper wire will 

 slightly diminish it, still, the specific resistance of copper compared with 

 nickel being in the ratio of 1 : 7"7, a comparison is possible. For strict 

 comparison the magnetic field in which the copper is tested should be 

 stronger than the field round the nickel when tested ; this will be done when 

 stronger fields are available. The copper wire had on a longitudinal load of 

 2 x 10 5 grammes per sq. cm., and the subsidence of torsional oscillations was 

 observed in transverse magnetic fields of values H = 0, H = 200 D.C., 

 H = 200 A.G. (n = 50) and H = 65 A.C. (n = 50) and (n = 200), and the 

 curves obtained in the five cases were precisely identical. It may be 

 concluded therefore (for transverse magnetic fields up to 200 units) that 

 eddy currents in the wire have little or no effect on the damping of the 

 torsional oscillations. 



For assistance in wiring up the apparatus, and in making some of the 

 observations, I am indebted to Mr. E. Macaulay, the Electrician at the Royal 

 College of Science. 



